The Pathology Core is responsible (1) for accrual of residual material not required for diagnosis from human melanomas and nevi for use in the Projects;(2) for the provision of expert pathological assistance in the interpretation of histological data to the Projects;and (3) for the development of immunohistochemical, in situ hybridization, microdissection and mRNA amplification methods to enable the identification of antigens or mRNAs in archival and freshly-isolated tissues. Many antibodies and/or probes of relevance to the projects in this proposal are available with reqactivity in fixed or frozen tissue. The Core has access to a very large collection of human tissue biopsies including thousands of pigmented lesions in the affiliated laboratories of Surgical Pathology (23,000 accessions/year) and of dermatopathology (50,000). The database of the Pigmented Lesion Group including glass slides of virtually all of the >4000 cases of primary accrued by the Group since 1972 is available to the Core for analysis of attributes to be used in model-building, and for selection of blocks to be retrieved from the permanent archives of our own laboratories and of contributing laboratories. Expertise in all aspects of the pathological diagnosis and classification of melanocytic neoplasms is provided to the projects on a continuing basis.